Acoustic wave element

Abstract

An acoustic wave element includes an IDT electrode including electrode fingers, a first substrate on an upper surface of which the IDT electrode is located, which has a thickness of less than 2 times a repetition interval of the electrode fingers and is configured by a piezoelectric crystal, a second substrate bonded to a lower surface of the first substrate, and configured by an Si single crystal having a plane orientation of a (100) plane or (110) plane or a plane equal to them, in which substrate a crystal axis of the Si single crystal parallel to a substrate surface of Si single crystal is inclined at any angle of 25° to 65°, 115° to 155°, 205° to 245°, and 295° to 345° relative to a direction of propagation of an acoustic wave when viewed from the upper surface of the superposed first substrate.

The invention claimed is: 
     
       1. An acoustic wave element comprising:
 an IDT electrode comprising a plurality of electrode fingers and exciting a surface acoustic wave, 
 a first substrate, which is a lithium tantalite single crystal substrate, on an upper surface of which the IDT electrode is located, which has a thickness of less than a wavelength λ, of the surface acoustic wave defined by 2 times a repetition interval of the plurality of electrode fingers and is configured by a piezoelectric crystal, 
 a second substrate which is directly or indirectly bonded to a lower surface of the first substrate and is configured by a material satisfying equation (1) where an acoustic impedance is I (Mrayl) and a transverse acoustic wave velocity is V (m/s):
   −0.0085× V+ 45.75≤ I≤− 0.0085× V+ 65.75  (1)
 
 
 an intermediate layer between the first substrate and the second substrate, wherein
 the intermediate layer comprises a first surface and a second surface, the first surface bonded to the lower surface of the first substrate, and is configured by a material having a slower transverse acoustic wave velocity than that of the first substrate, and 
 the second substrate is faster in transverse acoustic wave velocity than the first substrate and the intermediate layer, and 
 the second substrate is configured by an Si single crystal with a plane orientation of (100), in which when Euler angles are (φ, θ, ψ), ψ becomes any of −30° to 30°, 60° to 120°, 150° to 210°, and 240° to 300° in relation to the direction of propagation in the superposed first substrate. 
 
 
     
     
       2. The acoustic wave element according to  claim 1 , wherein a resistivity of the second substrate is 5000 Ω·cm or more. 
     
     
       3. The acoustic wave element according to  claim 1 , wherein the thickness of the first substrate is in a range of 0.2λ to 0.8λ. 
     
     
       4. The acoustic wave element according to  claim 1 , wherein the intermediate layer is configured by a material having a smaller dielectric constant than that of the second substrate. 
     
     
       5. The acoustic wave element according to  claim 1 , wherein
 the intermediate layer is configured by silicon oxide and has a thickness of 0.02λ to 0.08λ. 
 
     
     
       6. The acoustic wave element according to  claim 1 , wherein:
 the intermediate layer is configured by silicon oxide and has a thickness of 0.1λ or more. 
 
     
     
       7. The acoustic wave element according to  claim 1 , wherein
 the intermediate layer is configured by silicon oxide, a thickness thereof is 0.1λ or more, and 
 a resistivity of the second substrate is 1000 Ω·cm or more. 
 
     
     
       8. The acoustic wave element according to  claim 1 , wherein
 the intermediate layer is configured by silicon oxide, a thickness thereof is 0.05λ, or more, and 
 a resistivity of the second substrate is 5000 Ω·cm or more. 
 
     
     
       9. The acoustic wave element according to  claim 1 , wherein the first substrate is an X-propagated, rotated, and Y-cut lithium tantalate single crystal substrate. 
     
     
       10. The acoustic wave element according to  claim 1 , wherein the thickness of the first substrate is greater than 0.2λ and is 0.6λ or less. 
     
     
       11. The acoustic wave element according to  claim 1 , further comprising:
 an insulation layer which is located on the upper surface of the first substrate and is configured by a material having a smaller dielectric constant than that of the first substrate and 
 an electrode layer which is located on the insulation layer and is electrically connected with the IDT electrode. 
 
     
     
       12. The acoustic wave element according to  claim 1 , wherein
 when a pitch of the electrode fingers is “p”, the thickness D of the first substrate and the Euler angles of the second substrate satisfy a following relationship
   20× D+ 10+90×α≤ψ≤−20× D+ 80+90×α, and
 
   0.4 p≤D≤ 0.8 p,    
 
 where, α=0, 1, 2, 3. 
 
     
     
       13. An acoustic wave element comprising:
 an IDT electrode comprising a plurality of electrode fingers and exciting a surface acoustic wave, 
 a first substrate, which is a lithium tantalite single crystal substrate, on an upper surface of which the IDT electrode is located, which has a thickness of less than a wavelength λ of the surface acoustic wave defined by 2 times of a repetition interval of the plurality of electrode fingers and is configured by a piezoelectric crystal, 
 an intermediate layer which comprises a first surface and a second surface, the first surface bonded to a lower surface of the first substrate, and which is configured by a material having a slower transverse acoustic wave velocity than that of the first substrate, and 
 a second substrate is bonded to the second surface and is configured by an Si single crystal with a plane orientation of (100), in which when Euler angles are (φ, θ, ψ), ψ becomes any of −30° to 30°, 60° to 120°, 150° to 210°, and 240° to 300° in relation to the direction of propagation in the superposed first substrate. 
 
     
     
       14. The acoustic wave element according to  claim 13 , wherein the intermediate layer is configured by silicon oxide and has a thickness of 0.04λ, to 0.06λ. 
     
     
       15. The acoustic wave element according to  claim 13 , wherein:
 the intermediate layer is configured by silicon oxide, and 
 when the pitch of the electrode fingers is “p”, the thickness D of the first substrate and the Euler angles of the second substrate satisfy a following relationship
   22.86× D+ 8.48+90×α≤ψ≤−22.86× D+ 81.52+90×α, and
 
   0.4 p≤D≤ 0.9 p,    
 
 where, α=0, 1, 2, 3.